Process for making high denier filaments of thermotropic liquid crystalline polymers and compositions thereof

ABSTRACT

The present invention discloses and claims a novel process for the formation of high denier as-spun and heat-treated filaments of a thermotropic liquid crystalline polymer. Preferred embodiments include process for the formation of as-spun and heat treated monofilaments of a few wholly aromatic polyesters and polyesteramides. The process involves (a) heating of a thermotropic liquid crystalline polymer to above its melting transition temperature; (b) passing said molten polymer through an extrusion chamber equipped with an extrusion capillary of an aspect ratio of greater than about 1 and less than about 15 to form a filament; and (c) winding the filament at a draw-down ratio of at least about 4. The filaments so formed are of at least 50 denier per filament (dpf) and feature essentially uniform molecular orientation across the cross-section. In a final optional step, the filaments are heat treated in stages to form filaments exhibiting excellent tensile properties. Both as-spun and heat-treated filaments feature remarkably good tensile properties retaining at least 80 to 90 percent of the properties expected of conventional low denier (5 to 10 dpf) filaments.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to processes for forming filaments of athermotropic liquid crystalline polymer. Specifically, the presentinvention provides processes for forming as-spun and heat-treated highdenier filaments of a variety of thermotropic liquid crystalline whollyaromatic polyesters and polyesteramides. This invention also relates toas-spun and heat-treated high denier filaments of thermotropic liquidcrystalline polyesters and polyesteramides.

2. Description of the Prior Art

Thermotropic liquid crystalline polymers (LCPs) are an important classof polymers, which are generally wholly aromatic molecules containing avariety of heteroatom linkages including ester and/or esteramidelinkages. Upon heating to sufficiently high temperature, LCPs melt toform a liquid crystalline melt phase (often referred to as “anisotropicphase”) rather than an isotropic melt. Generally, LCPs consist of linear(“rigid rod”) molecules that can line up to yield the desired liquidcrystalline order. As a result, LCPs feature low melt viscosity and thusimproved performance and processabilities.

Because LCPs orient to form “rigid rod” linear molecules, LCPs exhibitextremely high mechanical properties. Thus, it is well known in the artthat LCPs can be formed into shaped articles, such as films, rods,pipes, fibers, and various other molded articles. In addition, it isalso known in the art that LCPs, particularly in the fiber form, exhibitexceptionally high mechanical properties after a heat treatment process.However, all of the known methods in the art describe formation of onlythe low denier fibers, e.g., of about 10 deniers per filament (dpf),which exhibit high mechanical properties in their as-spun as well asheat-treated forms.

Thus it is an object of the present invention to provide a process forforming uniformly oriented high denier LCP filaments. The high denierfilament means a filament of higher than 50 dpf

It is also an object of the present invention to provide a process forforming high denier LCP filaments of higher than 50 dpf, which exhibitenhanced mechanical, thermal and chemical resistance properties in theas-spun as well as heat-treated form.

It is further an object of the present invention to provide a processfor forming high denier LCP filaments, which exhibit propertiescomparable to those of low denier LCP filaments (i.e., filaments of lessthan 10 dpf) in their as-spun as well as heat treated states.

It is also an object of the present invention to provide high denier LCPfilaments of higher than 50 dpf having properties comparable to those oflow denier LCP filaments of less than 10 dpf

Finally, it is an object of the present invention to provide acost-effective, industrially economic way to heat-treat the high denierfilaments of this invention directly on the bobbin to produce highdenier filaments of superior mechanical and physical properties.

There is high desirability in forming uniformly oriented high denier LCPfilaments, which exhibit enhanced mechanical, thermal and chemicalresistance properties in the as-spun as well as heat-treated form. Forexample, high denier LCP filaments can replace steel wires in steelbelted tires. Furthermore, since LCP filaments are of substantiallylower density when compared with steel wires, LCP filaments are expectedto feature much superior properties than that exhibited by the steelwires. It is further obvious from the following prior art that there isa real need for high denier LCP filaments that exhibit enhancedmechanical, thermal, and chemical resistance properties.

Prior Art

The following references are disclosed as background prior art.

U.S. Pat. No. 4,183,895 describes a process for treating anisotropicmelt forming polymeric products. A process of heat treatment obtainedthe fibers having enhanced mechanical properties and the fiber tenacitywas increased by at least 50% and to at least 10 grams per denier.

U.S. Pat. No. 4,468,364 teaches a process for extruding thermotropicliquid crystalline polymers (LCPs). It is claimed that extrusion of anLCP through a die orifice having an L/D ratio of less than 2 (preferably0), and at a draw-down ratio of less than 4 (preferably 1), one canobtain filaments featuring high mechanical properties.

U.S. Pat. No. 4,910,057 describes a highly elongated member ofsubstantially uniform cross-sectional configuration, which is capable ofimproved service as a stiffening support in an optical fiber cable.

U.S. Pat. No. 5,246,776 teaches an aramide monofilament and method ofmaking the same.

U.S. Pat. No. 5,427,165 describes a reinforcement assemblage formed atleast in part of continuous monofilaments of liquid crystal organicpolymer(s). The polymers used therein are primarily aramids.

Japanese laid open Patent No. 4-333616 teaches a method of manufacturingfilaments of 50 to 2000 dpf from molten liquid crystalline polymers. Theheat-treated mechanical properties of these filaments were significantlyinferior than the properties reported for the corresponding lower denierfilaments of 5 to 10 dpf.

J. Rheology 1992, Vol. 36 (p. 1057-1078) reports a study of the rheologyand orientation behavior of a thermotropic liquid crystalline polyesterusing capillary dies of different aspect ratios.

J. Appl. Polym. Sci. 1995, Vol. 55 (p. 1489-1493) reports orientationdistribution in extruded rods of a thermotropic liquid crystallinepolyesters. The orientation function increases with increasing apparentshear rate from 166 to 270 sect⁻¹, but decreases with increasingapparent shear rate from 566 to 780 sec⁻¹.

All of the references described herein are incorporated herein byreference in their entirety.

SUMMARY OF THE INVENTION

Unexpectedly and surprisingly it has now been found that both as-spunand heat-treated high denier filaments of at least 50 denier perfilaments can be made that feature essentially uniform molecularorientation across the cross-section. Furthermore, these high denierfilaments feature remarkably good tensile properties retaining at least80 to 90 percent of the properties expected of conventional low denier—5to 10 dpf-filaments, which was hitherto unattainable by any of the knownprior art references as briefly described hereinabove.

Thus, in accordance with this invention there is provided a process forforming an as spun filament of a thermotropic liquid crystalline polymerhaving the following properties:

(i) denier of at least about 50 denier per filament;

(ii) tenacity of at least about 8 grams per denier;

(iii) modulus of at least about 450 grams per denier; and

(iv) elongation of at least about 2 percent.

The process of the present invention is comprised of the followingsteps:

(a) heating a thermotropic liquid crystalline polymer to a temperatureof at least about 15° C. above its melting transition to form a fluidstream of said thermotropic polymer;

(b) passing said stream through a heated extrusion chamber, wherein saidchamber is disposed with a suitable cylindrical orifice to form thefilament of said polymer, and wherein said cylindrical orifice has anaspect ratio of length to diameter (L/D) greater than about 1 and lessthan about 15; and

(c) winding said filament at a take-up speed of at least about 200meters per minute and draw-down (DD) ratio of at least about 4; and withthe proviso that when L/D is between 0 to 2, the DD is at least 4 so asto form the filament of essentially uniform molecular orientation acrossits cross-section and having a denier of at least about 50 denier perfilament.

In another aspect of the invention there is also provided a process forforming a heat-treated filament of a thermotropic liquid crystallinepolymer having the following properties:

(i) denier of at least about 50 denier per filament;

(ii) tenacity of at least about 20 grams per denier;

(iii) modulus of at least about 600 grams per denier; and

(iv) elongation of at least about 3 percent.

Thus in accordance with this aspect of the present invention, theprocess is comprised of the following steps:

(a) heating a thermotropic liquid crystalline polymer to a temperatureof about 15° C. to about 50° C. above its melting transition to form afluid stream of said polymer;

(b) extruding said stream of polymer through a heated cylindricalspinneret having at least one extrusion capillary to form a filament,wherein said capillary has an aspect ratio of length to diameter (L/D)in the range of from about 1 to about 10;

(c) winding said filament at a take-up speed of at least about 200meters per minute and draw-down ratio of from about 5 to about 40 so asto form a filament of essentially uniform molecular orientation acrossthe cross-section and having a denier in the range of from about 50 toabout 1000 denier per filament; and

(d) heat-treating said filament at suitable temperature and pressureconditions for a sufficient period of time, optionally in the presenceof an inert atmosphere, to form the heat-treated filament.

In yet another aspect of this invention there is also provided anas-spun filament of a thermotropic liquid crystalline polymer.

In a further aspect of this invention there is also provided aheat-treated filament of a thermotropic liquid crystalline polymer.

In another facet of this invention there is also provided a process forheat treating the high denier filaments of this invention directly onthe bobbin on which they were wound while spinning.

Other aspects and advantages of the present invention are describedfurther in the following detailed description of the preferredembodiments thereof.

Examples of the aromatic-aliphatic polyesters and polyesteramides whichmay be used in practicing the invention may include those having thefollowing structures.

I is

II is

III is

IV is

V is

VI is

and

VII is

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention there is provided a process forforming a filament of a thermotropic liquid crystalline polymer havingthe following properties:

(i) denier of at least about 50 denier per filament;

(ii) tenacity of at least about 8 grams per denier;

(iii) modulus of at least about 450 grams per denier; and

(iv) elongation of at least about 2 percent.

The process of the present invention is comprised of the followingsteps:

(a) heating a thermotropic liquid crystalline polymer to a temperatureof at least about 15° C. above its melting transition to form a fluidstream of said thermotropic polymer;

(b) passing said stream through a heated extrusion chamber, wherein saidchamber is disposed with a suitable cylindrical orifice to form thefilament of said polymer, and wherein said cylindrical orifice has anaspect ratio of length to diameter (L/D) greater than about 1 and lessthan about 15; and

(c) winding said filament at a take-up speed of at least about 200meters per minute and draw-down (DD) ratio of at least about 4; and withthe proviso that when L/D is between 0 to about 2, the DD is at least 4so as to form the filament of essentially uniform molecular orientationacross its cross-section and having a denier of at least about 50 denierper filament.

As discussed hereinabove, prior art references disclose variousprocesses for the manufacture of filaments of thermotropic polymers,including high denier filaments. A specific example of a method toprepare high denier filaments is disclosed in U.S. Pat. No. 4,468,364,which is incorporated herein by reference in its entirety. In this work,the thermotropic polymers were extruded from larger diameter jets at lowdraw-downs which automatically gave thicker filaments. The polymer meltwas also extruded at low throughputs, i.e., speed of polymer in the jet,and taking the filaments up at low speed. This means that most of theorientation of the filament is obtained from the converging flow in thejet itself which explains why increasing the capillary length causes areduction in orientation, i.e. orientation or filament modulus. Passageof the polymer through the capillary prior to exiting the jet will leadto disorientation of the flow which had been induced by the convergingpart of the jet above the capillary.

Unlike the process conditions of the prior art discussed hereinabove,the process of the present invention operates at higher draw-downs withthe result that the filament undergoes elongation to decrease thefilament diameter once it emerges from the jet orifice. Thiselongational flow puts most of the orientation into the filament, thusproviding a filament having essentially uniform cross-sectionalorientation.

Furthermore, the present invention also provides a commerciallypractical process in which the polymer throughput can be increased.Because the pressure over the jet will increase linearly withthroughput, the pressure will reach impractical levels for small jets.

In accordance with the process of the present invention, the preferredpolymers are thermotropic liquid crystalline polymers. Thermotropicliquid crystal polymers are polymers which are liquid crystalline (i.e.,anisotropic) in the melt phase. Thermotropic liquid crystal polymersinclude wholly aromatic polyesters, aromatic-aliphatic polyesters,aromatic polyazomethines, aromatic polyesteramides, aromaticpolyarmides, and aromatic polyester-carbonates. The aromatic polyestersare considered to be “wholly” aromatic in the sense that each moietypresent in the polyester contributes at least one aromatic ring to thepolymer backbone.

Specific examples of suitable aromatic-aliphatic polyesters arecopolymers of polyethylene terephthalate and hydroxybenzoic acid asdisclosed in Polyester X7G-A Self Reinforced Thermoplastic, by W. J.Jackson, Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th AnniversaryTechnical Conference, 1975 Reinforced Plastics/Composites Institute, TheSociety of the Plastics Industry, Inc., Section 17-D, Pages 1-4. Afurther disclosure of such copolymer can be found in “Liquid CrystalPolymers: I. Preparation and Properties of p-Hydroxybenzoic AcidCopolymers,” Journal of Polymer Science, Polymer Chemistry Edition, Vol.14, pp. 2043-58 (1976), by W. J. Jackson, Jr. and H. F. Kuhfuss. Theabove-cited references are herein incorporated by reference in theirentirety.

Aromatic polyazomethines and processes of preparing the same aredisclosed in the U.S. Pat. Nos. 3,493,522; 3,493,524; 3,503,739;3,516,970; 3,516,971; 3,526,611; 4,048,148; and 4,122,070. Each of thesepatents is herein incorporated by reference in its entirety. Specificexamples of such polymers includepoly(nitrilo-2-methyl-1,4-phenylenenitriloethylidyne-1,4-phenyleneethylidyne);poly(nitrilo-2-methyl-1,4-phenylene-nitrilomethylidyne-1,4-phenylenemethylidyne);andpoly(nitrilo-2-chloro-1,4-phenylenenitrilomethylidyne-1,4-phenylene-methylidyne).

Aromatic polyesteramides are disclosed in U.S. Pat. Nos. 5,204,443,4,330,457, 4,966,956, 4,355,132, 4,339,375, 4,351,917 and 4,351,918.Each of these patents is herein incorporated by reference in itsentirety. Specific examples of such polymers include polymer formed fromthe monomers comprising 4-hydroxybenzoic acid, 2,6-hydroxynaphthoicacid, terephthalic acid, 4,4′-biphenol, and 4-aminophenol; and polymerformed from the monomers comprising 4-hydroxybenzoic acid,2,6-naphthalene dicarboxylic acid, terephthalic acid, isophthalic acid,hydroquinone, and 4-aminophenol.

Preferred aromatic polyamides are those which are melt processable andform thermotropic melt phase as described hereinabove. Specific examplesof such polymers include polymer formed from the monomers comprisingterephthalic acid, isophthalic acid, and 2,2′-bis(4-aminophenyl)propane.

Aromatic polyester-carbonates are disclosed in U.S. Pat. No. 4,107,143,which is herein incorporated by reference in its entirety. Examples ofsuch polymers include those consisting essentially of hydroxybenzoicacid units, hydroquinone units, carbonate units, and aromatic carboxylicacid units.

The liquid crystal polymers which are preferred for use in the processof the present invention are the thermotropic wholly aromaticpolyesters. Specific examples of such polymers may be found in U.S. Pat.Nos. 3,991,013; 3,991,014; 4,057,597, 4,066,620; 4,075,262; 4,118,372;4,146,702; 4,153,779; 4,156,070; 4,159,365; 4,169,933; 4,181,792; and4,188,476, and U.K. Application No. 2,002,404. Each of these patents isherein incorporated by reference in its entirety.

Wholly aromatic polyesters which are preferred for use in the presentinvention are disclosed in commonly-assigned U.S. Pat. Nos. 4,067,852;4,083,829; 4,130,545; 4,161,470; 4,184,996; 4,238,599; 4,238,598;4,230,817; 4,224,433; 4,219,461; and 4,256,624. The disclosures of allof the above-identified commonly-assigned U.S. patents and applicationsare herein incorporated by reference in their entirety. The whollyaromatic polyesters disclosed therein typically are capable of formingan anisotropic melt phase at a temperature below approximately 350° C.

The wholly aromatic polyesters which are suitable for use in the processof the present invention may be formed by a variety of ester-formingtechniques whereby organic monomer compounds possessing functionalgroups which upon condensation form the requisite recurring moieties arereacted. For instance, the functional groups of the organic monomercompounds may be carboxylic acid groups, hydroxyl groups, ester groups,acyloxy groups, acid halides, etc. The organic monomer compounds may bereacted in the absence of a heat exchange fluid via a melt acidolysisprocedure. They, accordingly, may be heated initially to form a meltsolution of the reactants with the reaction continuing as solid polymerparticles are suspended therein. A vacuum may be applied to facilitateremoval of volatiles formed during the final stage of the condensation(e.g., acetic acid or water).

In commonly-assigned U.S. Pat. No. 4,083,829, entitled “Melt ProcessableThermotropic Wholly Aromatic Polyester,” is described a slurrypolymerization process which may be employed to form the wholly aromaticpolyesters which are preferred for use in the present invention.According to such a process, the solid product is suspended in a heatexchange medium. The disclosure of this patent has previously beenincorporated herein by reference in its entirety.

When employing either the melt acidolysis procedure or the slurryprocedure of U.S. Pat. No. 4,083,829, the organic monomer reactants fromwhich the wholly aromatic polyesters are derived may be initiallyprovided in a modified form whereby the usual hydroxy groups of suchmonomers are esterified (i.e., they are provided as lower acyl esters).The lower acyl groups preferably have from about two to about fourcarbon atoms. Preferably, the acetate esters of organic monomerreactants are provided.

Representative catalysts which optionally may be employed in either themelt acidolysis procedure or in the slurry procedure of U.S. Pat. No.4,083,829 include dialkyl tin oxide (for example, dibutyl tin oxide),diaryl tin oxide, titanium dioxide, antimony trioxide, alkoxy titaniumsilicates, titanium alkoxides, alkali and alkaline earth metal salts ofcarboxylic acids (for example, zinc acetate), gaseous acid catalystssuch as Lewis acids (for example, BF₃), hydrogen halides (for example,HCl), and similar catalyst known to one skilled in the art. The quantityof catalyst utilized typically is about 0.001 to about 1 percent byweight based upon the total monomer weight, and most commonly about 0.01to about 0.2 percent by weight.

The wholly aromatic polyesters which are preferred for use in thepresent invention commonly exhibit a weight average molecular weight ofabout 10,000 to about 200,000, and preferably about 20,000 to about50,000, (for example, about 30,000 to about 40,000). Such molecularweight may be determined by commonly used techniques, such as, gelpermeation chromatography or solution viscosity measurements. Othermethods include end group determination via infrared spectroscopy oncompression molded films or nuclear magnetic resonance spectroscopic(NMR) measurements of polymeric solutions or solid phase NMR of polymerpowder or films. Alternatively, light scattering techniques in apentafluorophenol solution may be employed to determine the molecularweight.

The wholly aromatic polyesters or polyesteramides additionally commonlyexhibit an inherent viscosity (i.e., I.V.) of at least about 2.0 dL/g,for example, about 2.0 to about 10.0 dL/g, when dissolved in aconcentration of 0.1 percent by weight in a 1:1 solvent mixture ofhexafluoroisopropanol(HFIP)/pentafluorophenol (PFP) (v/v) at 25° C.

Especially preferred polymers for the process of this invention arewholly aromatic polyesters and polyesteramides. In preferred embodimentsof this invention, specifically preferred polyesters are listed below:

a) The wholly aromatic polyester capable of forming an anisotropic meltphase at a temperature below approximately 350° C. consistingessentially of the recurring moieties I and II wherein:

I is

and

II is

The wholly aromatic polyester as described above is disclosed in U.S.Pat. No. 4,161,470. The polyester comprises about 10 to about 90 molepercent of moiety I, and about 10 to about 90 mole percent of moiety II.In one embodiment, moiety II is present in a concentration of about 65to about 85 mole percent, and preferably in a concentration of about 70to about 80 mole percent; for example, about 75 mole percent. In anotherembodiment, moiety II is present in a lesser proportion of about 15 toabout 35 mole percent, and preferably in a concentration of about 20 toabout 30 mole percent.

b) The wholly aromatic polyester capable of forming an anisotropic meltphase at a temperature below approximately 400° C. consistingessentially of the recurring moieties I, II, III, and VII wherein:

I is

II is

III is

and

VII is

The polyester comprises about 40 to about 60 mole percent of moiety I,about 2 to about 30 mole percent of moiety II, and about 19 to about 29mole percent each of moieties III and VII. In one of the preferredembodiments, the polyester comprises about 60 to about 70 mole percentof moiety I, about 3 to about 5 mole percent of moiety II, and about12.5 to about 18.5 mole percent each of moieties III and VII.

The preferred polyesteramides of the process of the present inventionare summarized below:

a) The wholly aromatic polyesteramide capable of forming an anisotropicmelt phase at a temperature below approximately 360° C. consistingessentially of the recurring moieties II, I III, and VI wherein:

II is

IIII is

and

VI is

The wholly aromatic polyesteramide as described above is disclosed inU.S. Pat. No. 4,330,457, which is hereby incorporated herein byreference in its entirety. The polyesteramide comprises about 25 toabout 75 mole percent of moiety II, about 37.5 to about 12.5 molepercent each of moieties I III and VI. The polyesteramide preferablycomprises about 40 to about 70 mole percent of moiety II, and about 15to about 30 mole percent each of moieties I III and VI. In one of thepreferred embodiments of this invention, the polyesteramide comprisesabout 60 to about 65 mole percent of moiety II, and about 17.5 to about20 mole percent each of moieties I III, and VI.

b) The wholly aromatic polyesteramide capable of forming an anisotropicmelt phase at a temperature below approximately 380° C. consistingessentially of the recurring moieties I, II, III, VII and VI wherein:

I is

II is

III is

VII is

and

VI is

The wholly aromatic polyesteramide as described above is disclosed inU.S. Pat. No. 5,204,443, which is hereby incorporated herein byreference in its entirety. The polyesteramide comprises approximately 40to 70 mole percent of moiety I, about 1 to about 20 mole percent ofmoiety II, about 14.5 to about 30 mole percent of moiety III, about 7 toabout 27.5 mole percent of moiety VII, and about 2.5 to about 7.5 molepercent of moiety VI.

c) The wholly aromatic polyesteramide capable of forming an anisotropicmelt phase at a temperature below approximately 350° C. consistingessentially of the recurring moieties I, II, III, IV, V, and VI wherein:

I is

II is

III is

IV is

V is

and

VI is

The polyesteramide as described above, comprises about 40 to about 70mole percent of moiety 1, about 10 to about 20 mole percent of moietyII, about 2.5 to about 20 mole percent of moiety III, about 0 to about 3mole percent of moiety IV, about 12.5 to about 27.5 mole percent ofmoiety V and about 2.5 to about 7.5 mole percent of moiety VI.

According to the process of the present invention, a fluid stream ofliquid crystal polymer is provided to any conventional extrusionapparatus. This is achieved by heating the thermotropic liquidcrystalline polymer of the present invention to form a melt. Any of theknown methods to heat the polymer to form a melt can be employed in thisinvention. The particular apparatus used is not critical to theoperation of the process of the present invention, and any suitableapparatus may be used herein. One such apparatus which has been found tobe suitable for use with thermotropic liquid crystal polymers employs acontact melting method so that melt residence time can be kept short andconstant. The apparatus includes a heated surface against which a moldedrod of liquid crystal polymer is pressed. The fluid stream of moltenpolymer is then introduced to the extrusion chamber inside of which aredisposed a filter pack and a cylindrical orifice. After being passedthrough the filter pack, the polymer melt is extruded through thecylindrical orifice.

In a preferred embodiment, the extrusion chamber is comprised of asingle orifice cylindrical chamber in which the polymer is heated to atemperature in the range of about 20° C. to about 50° C. above itsmelting transition. In this preferred embodiment the cylindrical orificehaving an aspect ratio (L/D) of about 1 to about 10 is employed. As usedherein, the aspect ratio is meant to define the ratio of length (L) todiameter (D) of the cylindrical orifice. In a more preferred embodimentof this invention, the aspect ratio of the cylindrical orifice is in therange of about 1 to about 3.

After the fluid stream of the liquid crystal polymer is extruded throughthe orifice, the polymer forms an elongated shaped article having thepolymer molecules oriented substantially parallel to the flow direction.The orientation of the polymer molecules can be confirmed by determiningorientation angle by X-ray analysis. The extruded shaped articles in theform of filaments are then drawn-down and taken-up on a filament spool.In accordance with the process of this invention, it is critical thatthe appropriate draw-down ratio be used to exploit maximum benefit fromthe practice of this invention. Thus, in a preferred embodiment, thedraw-down ratio in the range of from about 4 to about 20 is employed. Ina more preferred embodiment, the draw-down ratio in the range of fromabout 4 to about 15 is employed. The draw-down ratio (DD) as used hereinis defined as the ratio of cross-sectional area of the orifice (A₁) tothe cross-sectional area of the filament (A₂). This ratio is often alsoexpressed as the ratio of the take-up speed of the filament (V₂) to theextrusion speed of the filament (V₁). Thus the draw-down ratio, DD, maybe expressed in terms of the following equation:

DD=A₁/A₂=V₂/V₁

Thus, in accordance with the process of the present invention,thermotropic liquid crystalline polymeric filaments having essentiallyuniform molecular orientation that exhibit unusually superior mechanicalproperties can be made. For example, by properly practicing the processof the present invention, it is now possible to obtain a high denierfilament having hitherto unattainable properties. More specifically, ithas now been found that filaments having a denier in the range of fromabout 100 to about 1000 denier per filament (dpf) can readily be made byfollowing the process of this invention. In a preferred embodiment,filaments having a denier in the range of from about 150 to about 500dpf can readily be made. In a more preferred embodiment, filamentshaving a denier in the range of from about 180 to about 300 dpf canreadily be made. The denier as used herein is defined as a weight ingrams of 9,000 meters of the filament. The dpf as used herein is thedenier of an individual continuous filament.

The conditions of temperature and pressure under which the liquidcrystal polymer can be extruded are not critical to the process of thepresent invention and can easily be determined by one of ordinary skillin the art. Typically, thermotropic polymers are extruded at atemperature of about 280° C. to about 400° C. and at a pressure of about100 p.s.i. to about 5,000 p.s.i.

As discussed hereinabove, liquid crystal polymers have very stiff,rod-like molecules. In the quiescent state, the polymer molecules lineup in local regions, thereby forming ordered arrays or domains. Theexistence of domain texture within the microstructure of a liquidcrystal polymer may be confirmed by conventional polarized lighttechniques whereby a polarizing microscope utilizing crossed-polarizersis employed.

The mechanical properties of filaments produced in accordance with theprocess of the present invention can be improved still further bysubjecting the articles to a heat treatment following extrusion. Thearticles may be thermally treated in an inert atmosphere (e.g.,nitrogen, argon, helium). For instance, the article may be brought to atemperature about 10° C. to about 30° C. below the melting temperatureof the liquid crystal polymer, at which temperature the filament remainsas a solid object. The heat treatment times commonly range from a fewminutes to a number of days, e.g., from about 0.5 to 200 hours, or more.Preferably, the heat treatment is conducted for a time of about 1 toabout 48 hours (e.g., about 24 to about 30 hours). The heat treatmentimproves the properties of the article by increasing the molecularweight of the liquid crystalline polymer and increasing the degree ofcrystallinity.

Thus, in accordance with one of the preferred embodiments of the presentinvention there is also provided a process for forming a heat-treatedfilament of a thermotropic liquid crystalline polymer having thefollowing properties:

(i) denier of at least about 50 denier per filament;

(ii) tenacity of at least about 20 grams per denier;

(iii) modulus of at least about 600 grams per denier; and

(iv) elongation of at least about 3 percent.

The process for forming such a filament is comprised of the followingsteps:

(a) heating a thermotropic liquid crystalline polymer to a temperatureof about 15° C. to about 50° C. above its melting transition to form afluid stream of said polymer;

(b) extruding said stream of polymer through a heated cylindricalspinneret 20 having at least one extrusion capillary to form a filament,wherein said capillary has an aspect ratio of length to diameter (L/D)in the range of from about 1 to about 10;

(c) winding said filament at a take-up speed of at least about 200meters per minute and draw-down ratio of from about 5 to about 40 so asto form a filament of essentially uniform molecular orientation acrossthe cross-section and having a denier in the range of from about 50 toabout 1000 denier per filament; and

(d) heat-treating said filament at suitable temperature and pressureconditions for a sufficient period of time, optionally in the presenceof an inert atmosphere, to form the heat-treated filament.

Any of the preferred thermotropic polyesters or polyesteramidesdescribed hereinabove may be used in this preferred embodiment. Further,as described herein, the heat treatment can be carried out in stages ata final temperature of about 15° C. below the melting transition of thethermotropic polymer.

In another preferred embodiment of this invention there is also providedan as-spun filament of a thermotropic liquid crystalline polymer havingthe following properties:

(a) denier of at least about 50 denier per filament;

(b) tenacity of at least about 8 grams per denier;

(c) modulus of at least about 450 grams per denier; and

(d) elongation of at least about 2 percent.

In a particularly preferred embodiment of this invention the denier ofas-spun filament is in the range of from about 100 to about 1000 dpf Ina more particularly preferred embodiment of this invention the denier ofas-spun filament is in the range of from about 150 to about 500 dpf. Ina most particularly preferred embodiment of this invention the denier ofas-spun filament is in the range of from about 180 to about 300 dpf.

In yet another preferred embodiment of this invention there is alsoprovided a heat-treated filament of a thermotropic liquid crystallinepolymer having the following properties:

(a) denier of at least about 50 denier per filament;

(b) tenacity of at least about 20 grams per denier;

(c) modulus of at least about 600 grams per denier; and

(d) elongation of at least about 3 percent.

In a further aspect of this invention there is also provided a processfor heat treating the high denier filaments produced in accordance ofthe process of this invention described hereinabove. In this aspect ofthe invention, the filaments wound on the bobbin are directly heattreated to obtain the heat-treated filaments, thus offering significantcost savings.

Thus, in accordance with this aspect of the invention, the process iscomprised of the following steps:

(a) heating a thermotropic liquid crystalline polymer to a temperatureof at least about 15° C. above its melting transition to form a fluidstream of said thermotropic polymer;

(b) passing said stream through a heated extrusion chamber, wherein saidchamber is disposed with a suitable cylindrical orifice to form thefilament of said polymer, and wherein said cylindrical orifice has anaspect ratio of length to diameter (L/D) greater than about 1 and lessthan about 15; and

(c) winding said filament on to a bobbin at a low tension of at leastabout 5 grams and take-up speed of at least about 200 meters per minuteand draw-down (DD) ratio of at least about 4 so as to form the filamentof essentially uniform molecular orientation across its cross-sectionand having a denier of at least about 50 denier per filament; and

(d) heat treating said filament directly on said bobbin at suitabletemperature and pressure conditions for a sufficient period of time,optionally in the presence of an inert atmosphere, to form the heattreated filament.

Thus, by practicing this aspect of the present invention, it is nowpossible to obtain a heat-treated filament having the followingproperties:

(i) denier of at least about 50 denier per filament;

(ii) tenacity of at least about 20 grams per denier;

(iii) modulus of at least about 600 grams per denier; and

(iv) elongation of at least about 3 percent.

Any of the thermotropic polymers described hereinabove may be used inthis aspect of the invention. Preferred thermotropic polymers are thepolyesters and polyesteramides as described hereinabove.

Surprisingly, it has now been found that applying low tension whilewinding the filament on to the bobbin markedly improves the tensileproperties of the filaments after heat treatment. For example, tensionsof about 5 grams to 30 grams appears to be essential. It is preferredthat tensions of about 10 grams is applied to obtain maximum benefitfrom the practice of this invention.

This invention is further illustrated by the following examples, whichare provided for illustration purposes and in no way limit the scope ofthe present invention.

EXAMPLES (GENERAL)

In the Examples that follow, the following abbreviations are used:

HBA=4-Hydroxybenzoic acid

HNA=2,6-Hydroxynaphthoic acid

TA=Terephthalic acid

IA=Isophthalic acid

NDA=2,6-Naphthalene dicarboxylic acid

BP=4,4′-Biphenol

HQ=Hydroquinone

AA=1-Acetoxy-4-acetamidobenzene

IV=Inherent viscosity

dL/g=deciliters per gram; an unit of measure of IV

wt. %=weight per cent; generally used to represent the concentration ofa solution to measure IV—means grams of polymer in 100 mL of a solventmixture.

MV=Melt viscosity

DSC=Differential Scanning Calorimetry

T=Tenacity

M=Modulus

E=Elongation

gpd=grams per denier

General Analytical Techniques used for the Characterization of thePolymer

A variety of analytical techniques were used to characterize the polymerused and the filaments formed according to the present invention, whichincluded the following:

IV: The solution viscosity of the polymer samples, IV, was measured at25° C. in a concentration of 0.1 wt. % solution in equal parts by volumeof pentafluorophenol and hexafluoroisopropanol.

MV: MV of polymer samples was measured using a Kayeness Melt RheometerModel 2052 equipped with a Hastalloy barrel and plunger tip. The radiusof the die orifice was 0.015 inch and the length was 1 inch. For thepurpose of determining melt viscosity, a plot of viscosity vs. shearrate was generated by measuring the viscosities at shear rates of 56,166, 944, 2388, and 8333 sec⁻¹, and viscosities at 100 and 1000 sec⁻¹were interpolated.

DSC: DSC of polymer samples was performed on a Perkin Elmer 7700 ThermalAnalysis System. In all runs the samples, sealed in aluminum pans, wereheated or cooled at a rate of 20° C./min. under a nitrogen atmosphere.The DSC curves obtained from the second heating run were taken for theanalysis.

Light Microscopy: Samples were prepared for microscopic analysis by thinsectioning using a glass knife microtome. The sections were examined bypolarized light microscopy to observe morphological behavior at ambienttemperatures.

Example 1

This Example 1 demonstrates the general increase in mechanicalproperties of an as-spun high denier filament of a liquid crystallinewholly aromatic polyester produced in accordance with the presentinvention, i.e., filaments formed from a die having an aspect ratio(L/D) higher than 2 and at a draw-down ratio (DD) equal to or higherthan 4.

Filaments were formed from a thermotropic liquid crystalline whollyaromatic HBA/BA polyester sold under the tradename of “VECTRA™ A”(Ticona LLC, Summit, N.J.). This polymer exhibited a melting temperatureof 280° C. and an inherent viscosity of 6.30 dL/g when measured in aconcentration of 0.1 percent by weight solution in equal parts by volumeof pentafluorophenol and hexafluoroisopropanol at 25° C.

A sample of the polymer was dried overnight at 130° C. under vacuum. Thepolymer was melted in a 1 inch diameter extruder, and the extrudate wasmetered using a conventional polymer meter pump to the spinning packwhere it was filtered through 50/80 shattered metal. The melt was thenextruded through a single hole spinneret of various aspect ratios (L/D)as listed in Table 1. Crossflow quench was applied to the emergingfilament to provide cooling and a stable spinning environment. Thequench was situated 4 cm below the spinneret face, and was 120 cm longby 15 cm wide. The quench flow rate at the top was 30 mpm (0.5 mpsec).The monofilament was dressed either with water or with a spinning finishbefore passing around a system of godets which controlled the take-upspeed. It was finally taken up on a Sahm spool winder.

Mechanical properties of the monofilaments produced in accordance withthis Example 1 were measured in accordance with ASTM D3822, and theresults are listed in Table I. For purposes of comparison, monofilamentswere also extruded in the manner described above with the exception thatthe DD ratios were maintained below 4. In a few of these comparativeruns, spinnerets with low aspect ratios (L/D less than 2) were alsoused, as listed in Table I. Mechanical properties of these monofilamentswere measured using the same procedures as described above and are alsolisted in Table I.

The data given in Table I indicate a dramatic improvement in propertiesof monofilaments extruded with spinnerets having aspect ratio (L/D)higher than 1 and DD ratio higher than 4 as compared to those ofmonofilaments extruded with spinnerets having aspect ratio (L/D) lowerthan 2 and at DD ratios lower than 4. This Example thus demonstrates thebeneficial effects achieved by extruding liquid crystal polymer througha spinnerets having L/D higher than 2 at a draw-down ratio of higherthan 4 in accordance with the process of the present invention.

Note: In all Tables herein, all samples were tested at 10-inch gaugelength, 20% strain rate, 10 filament break.

TABLE I Sample No. L/D Draw-Down Denier (g) Tenacity (gpd) Modulus (gpd)Elongation (%) 38592-46-1 0 56.5 239 5.7 466 1.4 39592-49-1 0 3.0 2167.4 589 1.6 38445-37-7 1 6.2 219 9 615 1.8 38592-48-1 1 54.7 247 6.4 4751.5 38664-1-1  1 6.4 225 10.2 597 2 38592-43-1 2 17.3 231 8.5 587 1.838592-45-1 10  57.0 237 6 533 1.4 38592-47-2 10  2.3 276 8.8 466 2.4

Example 2

Monofilaments produced in accordance with Example 1 were subjected to aheat treatment in stages as follows. Heat treatment of short lengths ofthe monofilament was carried out on racks under zero tension in a flowof dry nitrogen using a programmed temperature profile. The programmedtemperature profiles of each of the heat treatment of monofilaments arelisted in Table II. The heat-treated monofilament was tested at 10 inchgauge length; 20% strain rate and 10 filament break. Following heattreatment, the mechanical properties of the monofilaments were measuredand are listed in Table II.

The measurements were made using the same tests as in Example 1. Thedata demonstrate the increase in properties, which is obtained bysubjecting the monofilaments to staged heat treatment conditions.

TABLE II Sample Preheat Orifice Size Den. Ten. Mod. Elong. NumberCondition Heat Treatment Condition (Draw-down) (g) (gpd) (gpd) (%)38543-02-1 230° C./2 hr 2 hr hold @ 270° C. 0.015″ (6.2)  207 25.64 6993.25 38543-02-3 230° C./2 hr 8 hr hold @ 270° C. 0.015″ (6.2)  211 25.64690 3.31 38543-02-5 230° C./2 hr 14 hr hold @ 270° C.  0.015″ (6.2)  21324.36 633 3.17 38543-03-1 None 2 hr hold @ 270° C. 0.015″ (6.2)  21121.69 621 3.03 38445-38-6 None As-Spun (Control) 0.025″ (17.1) 205 10.1593 1.88 38543-02-2 230° C./2 hr 2 hr hold @ 270° C. 0.025″ (17.1) 20122.45 682 3.04 38543-02-4 230° C./2 hr 8 hr hold @ 270° C. 0.025″ (17.1)203 24.76 641 3.25 38543-02-3 230° C./2 hr 14 hr hold @ 270° C.  0.025″(17.1) 213 23.44 613 3.31 38543-03-2 None 2 hr hold @ 270° C. 0.025″(17.1) 200 18.12 586 2.78

Example 3

Examples 1 and 2 were repeated in this Example 3 except that the highdenier filaments of Vectra A polymer were formed. The Table IIIsummarizes the as-spun and heat-treated properties of the filaments.

TABLE III Sample Orifice Size Den. Ten. Mod. Elong. Number HeatTreatment Condition (Draw-down) (g) (gpd) (gpd) (%) 38538-16-6 As-Spun0.015″ 228 10.4 546 2.0 38543-09-1 230° C./2 hr; 270° C./2 hr (6.2)  22822.3 608 3.2 38538-16-7 As-Spun 0.015″ 339 9.8 531 2.0 38543-09-2 230°C./2 hr; 270° C./2 hr (6.2)  334 18.8 625 2.5 38538-16-8 As-Spun 0.015″449 10.0 532 2.1 38543-09-3 230° C./2 hr; 270° C./2 hr (6.2)  439 17.1583 2.7 38538-20-3 As-Spun 0.025″ 461 9.5 543 2.0 38543-09-4 230° C./2hr; 270° C./2 hr (17.1) 454 18.5 648 2.8 38538-20-5 As-Spun 0.025″ 6679.0 540 1.9 38543-09-5 230° C./2 hr; 270° C./2 hr (17.1) 645 17.6 5622.8 38538-20-7 As-Spun 0.025″ 868 8.8 486 2.1 38543-09-6 230° C./2 hr;270° C./2 hr (17.1) 866 14.2 528 2.6

Example 4

Examples 1 and 2 were repeated in this Example 4 except that thethermotropic polyesteramide was employed in this Example 4. A HNA/AA/TApolyesteramide was used in Example 4 was sold under the tradename of“VECTRA™ B” (Ticona LLC, Summit, N.J.). The Table IV-A summarizes theas-spun and heat-treated properties of the high denier single filamentsformed from this polymer.

TABLE IV-A Sample Orifice Size Den. Ten. Mod. Elong. Number HeatTreatment Condition (Draw-down) (g) (gpd) (gpd) (%) 38445-44-2 As-Spun0.015″ 213 9.5 698 1.80 38543-06-1 2 hr Preheat @ 230° C., 0.015″ 21111.1 676 1.92 2 hr hold @ 270° C. 38543-06-3 2 hr Preheat @ 230° C.,0.015″ 208 16.8 697 2.60 2 hr hold @ 270° C. 38543-06-5 2 hr Preheat @230° C., 0.015″ 208 21.6 710 3.00 2 hr hold @ 270° C. 38445-44-4 As-Spun0.025″ 235 9.4 705 1.78 38543-06-2 2 hr Preheat @ 230° C., 0.025″ 22811.0 680 1.89 2 hr hold @ 270° C. 38543-06-4 2 hr Preheat @ 230° C.,0.025″ 228 17.1 702 2.59 2 hr hold @ 270° C. 38543-06-6 2 hr Preheat @230° C., 0.025″ 232 20.8 698 2.97 2 hr hold @ 270° C.

A few of the filament samples extruded from VECTRA™ B were also heattreated under optimal temperature and time conditions. The results ofwhich are listed in Table IV-B

TABLE IV-B Sample Orifice Size Den. Ten. Mod. Elong. Number HeatTreatment Condition (Draw-down) (g) (gpd) (gpd) (%) 38445-44-2 As-Spun0.015″ 213 9.5 698 1.80 38543-10-1 260° C./1 hr; 290° C./2 hr; 0.015″207 15.4 676 2.4 300° C./2 hr 38543-10-2 260° C./1 hr; 280° C./2 hr;0.015″ 204 24.9 705 3.6 300° C./2 hr 38543-10-3 260° C./1 hr; 270° C./2hr; 0.015″ 206 20.1 709 3.0 290° C./2 hr 38543-10-4 260° C./1 hr; 250°C./2 hr; 0.015″ 210 7.7 717 1.3 280° C./2 hr 38543-10-5 230° C./2 hr;270° C./18 hr 0.015″ 212 17.7 739 2.6 38445-44-4 As-Spun 0.025″ 235 9.4705 1.78 38543-10-6 230° C./2 hr; 270° C./18 hr 0.015″ 230 18.6 755 2.6

Example 5

Examples 1 and 2 were repeated in this Example 5 except that thethermotropic polyesteramide was employed in this Example 5. Thepolyesteramide used in this Example comprises HBA, HNA, TA, BP and AAunits, and is sold under the tradename of “VECTRA™ Ei” (Ticona LLC,Summit, N.J.). Table V summarizes the as-spun and heat-treatedproperties of the high denier single filaments formed from this polymer.

TABLE V Sample Orifice Size Number Heat Treatment Condition (Draw-down)Denier (g) Tenacity (gpd) Modulus (gpd) Elongation (%) 38445-49-8As-Spun 0.015″ 219 7.0 576 1.30 (6.2)  38543-07-1 No Preheat 0.015″ 21421.7 819 2.6 2 hr @ 300° C. (6.2)  38543-07-3 No Preheat 0.015″ 214 23.5837 2.5 6 hr @ 300° C. (6.2)  38543-07-5 No Preheat 0.015″ 210 23.6 8572.5 10 hr @ 300° C.  (6.2)  38538-01-1 As-Spun 0.025″ 227 6.6 608 1.15(17.1) 38543-07-2 No Preheat 0.025″ 216 19.8 838 2.2 2 hr @ 300° C.(17.1) 38543-07-4 No Preheat 0.025″ 222 21.2 856 2.2 6 hr @ 300° C.(17.1) 38543-07-6 No Preheat 0.025″ 230 21.4 841 2.3 10 hr @ 300° C. (17.1)

Example 6

Examples 1 and 2 were repeated in this Example 6 except that thethermotropic polyesteramide was employed in this Example 6. Thepolyesteramide used in this Example comprises HBA, HNA, TA, BP and AAunits, and is sold under the tradename of “VECTRA™ L” (Ticona LLC,Summit, N.J.). Table VI summarizes the as-spun and heat-treatedproperties of the high denier single filaments formed from this polymer.

TABLE VI Orifice Size Den. Ten. Mod. Elong. Sample No. Heat TreatmentCondition (Draw-down) (g) (gpd) (gpd) (%) 38538-25-1 As-Spun 0.015″ 2288.6 551 1.6 38543-11-1 230° C./2 hrs. 0.015″ 223 20.4 671 3.0 270° C./8hrs. (6.2)  38543-11-3 230° C./2 hrs. 0.015″ 225 21.7 697 2.6  270°C./16 hrs. (6.2)  38543-11-5 300° C./8 hrs. 0.015″ 221 19.0 607 2.7(6.2)  38538-26-1 As-Spun 0.025″ 233 7.5 564 1.5 (17.1) 38543-11-2 230°C./2 hrs. 0.025″ 227 17.1 673 2.4 270° C./8 hrs. (17.1) 38543-11-4 230°C./2 hrs. 0.025″ 225 18.5 687 2.3  270° C./16 hrs. (17.1) 38543-11-6300° C./8 hrs. 0.025″ 216 17.8 616 2.5 (17.1)

Example 7

In Example 7, VECTRA™ L filaments were prepared as in Example 6, exceptat higher denier. Draw-down was similar. Table VII summarizes theas-spun and heat-treated properties of the filament formed from thispolymer.

TABLE VII Heat Treated Properties for High Denier Vectra ™ L MonofilsOrifice Size Den. Ten. Mod. Elong. Sample No. Heat Treatment Condition(Draw-down) (g) (gpd) (gpd) (%) 38538-25-1 As-Spun (Control) 0.015″ 2288.6 551 1.6 38543-11-1 230° C./2 hr; 270° C./8 hr (6.2)  38538-26-6As-Spun (Control) 0.015″ 337 8.6 558 1.6 38543-00-1 230° C./2 hr; 270°C./8 hr (6.2)  38538-25-7 As-Spun (Control) 0.015″ 444 8.8 543 1.738543-00-0 230° C./2 hr; 270° C./8 hr (6.2)  38538-25-8 As-Spun(Control) 0.015″ 545 8.8 544 1.7 38543-00-0 230° C./2 hr; 270° C./8 hr(6.2)  38538-25-9 As-Spun (Control) 0.015″ 656 8.5 520 1.7 38543-00-0230° C./2 hr; 270° C./8 hr (6.2)   38534-25-10 As-Spun (Control) 0.015″745 8.1 510 1.7 38543-00-0 230° C./2 hr; 270° C./8 hr (6.2)  38538-26-1As-Spun (Control) 0.025″ 233 7.5 564 1.5 38543-00-0 230° C./2 hr; 270°C./8 hr. (17.1) 227 17.1 673 2.4 38538-26-6 As-Spun (Control) 0.025″ 3507.9 580 1.5 38543-00-0 230° C./2 hr; 270° C./8 hr (17.1) 38538-26-7As-Spun (Control) 0.025″ 467 8.0 551 1.6 38543-00-0 230° C./2 hr; 270°C./8 hr (17.1) 38538-26-8 As-Spun (Control) 0.025″ 578 7.8 534 1.638543-00-0 230° C./2 hr; 270° C./8 hr (17.1) 38538-20-9 As-Spun(Control) 0.025″ 676 7.3 530 1.6 38543-00-0 230° C./2 hr; 270° C./8 hr(17.1)  38538-20-10 As-Spun (Control) 0.025″ 781 7.3 501 1.6 38543-00-0230° C./2 hr; 270° C./8 hr (17.1)

Example 8

Example 8 demonstrates that the heat treatment of filament wounddirectly on-bobbin in accordance with one of the preferred embodimentsof this invention.

To develop the on-bobbin heat treatment capabilities, a heat treatmentsetup using a canister equipped with rubber gaskets was built. Aprogrammable forced air Precision oven with copper tubing running alongthe inside walls was used to heat the bobbins after it was placed andsealed in the canister. Nitrogen gas was introduced into the coppertubing at 60 to 100 SCFH, making sure that the nitrogen gas penetratesthe heat treatment package. The purge gas was heated as it passedthrough the oven tubing. The heated nitrogen was passed into thecanister and flowed from the center of the bobbin outward. The nitrogenwas then exhausted out of the canister and out of the oven guaranteeingthe removal of the reaction products which otherwise could inhibit theproperty buildup.

The heat treatment bobbins, 6-inch in diameter and about 13-inch wide,wask constructed of perforated aluminum cylinders. The outside of thecylinders were covered with fiberfrax, a porous ceramic matting, toaccommodate for the shrinkage of the monofilaments during heattreatment. For safety reasons (glass particulate containment), thefiberfrax was enclosed with polybenzimidazole (PBI) socks. Based onempirical findings, a permanent layer of Vectran™ yarn wrapped on top ofthe PBI enclosure offered better heat treated properties. To improvepackage formation (slough) for the monofilament processing, aluminumflanges were also added at each end of the bobbins. For bobbinpreparation, the as-spun monofilaments were wound on to the heattreatment bobbins at low tension by using a Leesona winder at 50 m/min.After heat treatment, the fiber was re-wound on to the final productspool.

For on-bobbin heat treatment, it was found that winding the fiber at lowtension is essential for making high tensile properties. By using lowrewind tension, low speed and fiber lubricant (finish or water),monofilaments with outstanding mechanical properties were obtained. Thestandard heat treatment process for monofilaments formed according tothe process of this invention is shown below. The initial dwell at 230°C. was added to allow the softening point to increase and eliminatefiber tapiness.

Heat Treatment Cycle:

(1)—Fast ramp to 230° C.

(2)—Dwell @230° C. for two hours

(3)—Ramp @15° C./hr. to 270° C.

(4)—Dwell @270° C. for 8 hours

(5)—Cool down to 100° C. before opening oven.

Monofilaments of VECTRA A were spun at 300 n/min and an appropriatedraw-down to make a 220 denier. For physical property enhancement, thefilaments were heat treated on the bobbin to make continuous heattreated monofilaments. Low tension during winding and rewinding is veryimportant in the determination of the final properties. For thisexperiment, approximately 10 grams of tension was considered as criticalduring winding on to the heat treatment bobbins in order to achieveoptimum properties while making a neat bobbin that can be heat treatedand unwound without any difficulty. Tensions lower than 10 gramsproduced bobbins in which the fiber was falling off the bobbin and weredifficult to unwound. The physical properties of samples rewound with 10grams of tension @50 m/m is as follows: Tenacity=25.89 g/d;Elongation=3.28% and Modulus=660.1 g/d.

Example 9

Example 8 was repeated in Example 9 with the exception that theincreased rewound tension of 20 grams was employed. The physicalproperties of the heat treated monofilament are as follows:

Tenacity=18.03 g/d; Elongation=2.50% and Modulus=650.8 g/d.

Example 10

Example 8 was repeated in this Example 10 with the exception that twoas-spun monofilament samples were taken-up directly (during spinning at300 m/min.) on to the heat treatment bobbins. The spinline tensions weremeasured as 10 and 20 grams with the physical properties shown below.

Sample No. 1: Sample as-spun to Leesona @300 m/m and 10 grams oftension:

Tenacity=20.3 g/d; Elongation=2.9%; Modulus=663 g/d

Sample No. 2: Sample as-spun to Leesona @300 m/m and 20 grams oftension:

Tenacity=15.6 g/d; Elongation=2.2%; Modulus=652 g/d

Examples 11

Comparison with a Conventional Process

Examples 1 and 2 were repeated in this Example 11, except that the highdenier VECTRA™ A polymer monofilaments were extruded using a water bathas the quench system. The extruded monofilaments were about 200 denierand were heat treated using the same system and conditions as Example 2.The results in the following Table VIII, summarizing the as-spun andheat-treated properties of the filaments, clearly indicate that thewater quenched monofilaments have inferior properties relative to thoseshown in Table II.

TABLE VIII Sample No. Heat Treatment Condition Denier (g) Tenacity (gpd)Mod. (gpd) Elong. (%) 38479-01-1 Control, as-spun 221 6.7 502 1.5838543-08-1 2 hr Preheat @ 230° C. 218 12.5 588 2.21 2 hr hold @ 270° C.38543-08-2 2 hr Preheat @ 230° C. 220 112.6 530 2.27 2 hr hold @ 270° C.

Although the invention has been illustrated by certain of the precedingexamples, it is not to be construed as being limited thereby; butrather, the invention encompasses the generic area as hereinbeforedisclosed. Various modifications and embodiments can be made withoutdeparting from the spirit and scope thereof.

I claim:
 1. A process for forming an as-spun filament of a thermotropicliquid crystalline polymer having the following properties: (i) denierof at least about 50 denier per filament; (ii) tenacity of at leastabout 8 grams per denier; (iii) modulus of at least about 450 grams perdenier; and (iv) elongation of at least about 2 percent; said processcomprising the steps of: (a) heating a thermotropic liquid crystallinepolymer to a temperature of at least about 15° C. above its meltingtransition to form a fluid stream of said thermotropic polymer; (b)passing said stream through a heated extrusion chamber, wherein saidchamber is disposed with a suitable cylindrical orifice to form thefilament of said polymer, and wherein said cylindrical orifice has anaspect ratio of length to diameter (L/D) greater than about 1 and lessthan about 15; and (c) winding said filament at a take-up speed of atleast about 200 meters per minute and draw-down (DD) ratio of at leastabout 4; and with the proviso that when L/D is between 0 to 2, the DD isat least 4 so as to form the filament of essentially uniform molecularorientation across its cross-section and having a denier of at leastabout 50 denier per filament.
 2. The process as set forth in claim 1,wherein said thermotropic liquid crystalline polymer is selected fromthe group consisting of wholly aromatic polyesters, aromatic-aliphaticpolyesters, aromatic polyazomethines, aromatic polyesteramides, aromaticpolyamides, and aromatic polyester-carbonates.
 3. The process as setforth in claim 1, wherein said thermotropic liquid crystalline polymeris a wholly aromatic polyester.
 4. The process as set forth in claim 3,wherein said polyester comprises a melt processable wholly aromaticpolyester capable of forming an anisotropic melt phase at a temperaturebelow approximately 350° C. consisting essentially of the recurringmoieties I and II wherein: I is

and II is

wherein said polyester comprises about 10 to about 90 mole percent ofmoiety I, and about 10 to about 90 mole percent of moiety II.
 5. Theprocess as set forth in claim 3, wherein said polyester comprises a meltprocessable wholly aromatic polyester capable of forming an anisotropicmelt phase at a temperature below approximately 400° C. consistingessentially of the recurring moieties I, II, III, and VII wherein: I is

II is

III is

and VII is

wherein said polyester comprises about 40 to about 70 mole percent ofmoiety I, about 1 to about 20 mole percent of moiety II, and about 14.5to about 30 mole percent each of moieties III and VII.
 6. The process asset forth in claim 1, wherein said thermotropic liquid crystallinepolymer is a wholly aromatic polyesteramide.
 7. The process as set forthin claim 6, wherein said polyesteramide comprises a melt processablewholly aromatic polyesteramide capable of forming an anisotropic meltphase at a temperature below approximately 360° C. consistingessentially of the recurring moieties II, I, III and VI wherein: II is

IIII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety II, and about 15 to about 30 mole percent each of moieties I,III and VI.
 8. The process as set forth in claim 6, wherein saidpolyesteramide comprises a melt processable wholly aromaticpolyesteramide capable of forming an anisotropic melt phase at atemperature below approximately 380° C. consisting essentially of therecurring moieties I, II, III, VII and VI wherein: I is

II is

III is

VII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 1 to about 20 mole percent of moiety II, about 14.5to about 30 mole percent of moiety III, about 7 to about 27.5 molepercent of moiety VII, and about 2.5 to about 7.5 mole percent of moietyVI.
 9. The process as set forth in claim 6, wherein said polyesteramidecomprises a melt processable wholly aromatic polyesteramide capable offorming an anisotropic melt phase at a temperature below approximately350° C. consisting essentially of the recurring moieties I, II, III, IV,V, and VI wherein: I is

II is

III is

IV is

V is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 10 to about 20 mole percent of moiety II, about 2.5to about 20 mole percent of moiety III, about 0 to about 3 mole percentof moiety IV, about 12.5 to about 27.5 mole percent of moiety V andabout 2.5 to about 7.5 mole percent of moiety VI.
 10. The process as setforth in claim 1, wherein said thermotropic liquid crystalline polymeris heated to a temperature of from about 20° C. to about 50° C. aboveits melting transition.
 11. The process as set forth in claim 1, whereinsaid aspect ratio (L/D) is from about 1 to about
 10. 12. The process asset forth in claim 1, wherein said aspect ratio (L/D) is from about 1 toabout
 3. 13. The process as set forth in claim 1, wherein said draw-downratio is from about 4 to about
 20. 14. The process as set forth in claim1, wherein said draw-down ratio is from about 4 to about
 15. 15. Theprocess as set forth in claim 1, wherein said filaments are amonofilament.
 16. The process as set forth in claim 15, wherein denierof said filament is from about 100 to about 1000 denier per filament.17. The process as set forth in claim 15, wherein denier of saidfilament is from about 150 to about 500 denier per filament.
 18. Theprocess as set forth in claim 15, wherein denier of said filament isfrom about 180 to about 300 denier per filament.
 19. The productproduced by the process of claim
 1. 20. The product produced by theprocess of claim
 4. 21. The product produced by the process of claim 5.22. The product produced by the process of claim
 7. 23. The productproduced by the process of claim
 8. 24. The product produced by theprocess of claim
 9. 25. The product produced by the process of claim 17.26. The product produced by the process of claim
 18. 27. A process forforming a heat-treated filament of a thermotropic liquid crystallinepolymer having the following properties: (i) denier of at least about 50denier per filament; (ii) tenacity of at least about 20 grams perdenier; (iii) modulus of at least about 600 grams per denier; and (iv)elongation of at least about 3 percent; said process comprising thesteps of: (a) heating a thermotropic liquid crystalline polymer to atemperature of about 15° C. to about 50° C. above its melting transitionto form a fluid stream of said polymer; (b) extruding said stream ofpolymer through a heated cylindrical spinneret having at least oneextrusion capillary to form a filament, wherein said capillary has anaspect ratio of length to diameter (L/D) in the range of from about 1 toabout 10; (c) winding said filament at a take-up speed of at least about200 meters per minute and draw-down ratio of from about 5 to about 40 soas to form a filament of essentially uniform molecular orientationacross the cross-section and having a denier in the range of from about50 to about 1000 denier per filament; and (d) heat-treating saidfilament at suitable temperature and pressure conditions for asufficient period of time, optionally in the presence of an inertatmosphere, to form the heat-treated filament.
 28. The process as setforth in claim 27, wherein said thermotropic liquid crystalline polymeris selected from the group consisting of: (i) a melt processable whollyaromatic polyester capable of forming an anisotropic melt phase at atemperature below approximately 350° C. consisting essentially of therecurring moieties I and II wherein: I is

and II is

wherein said polyester comprises about 10 to about 90 mole percent ofmoiety I, and about 10 to about 90 mole percent of moiety II; (ii) amelt processable wholly aromatic polyester capable of forming ananisotropic melt phase at a temperature below approximately 400° C.consisting essentially of the recurring moieties I, II, III, and VIIwherein: I is

II is

III is

and VII is

wherein said polyester comprises about 40 to about 70 mole percent ofmoiety I, about 1 to about 20 mole percent of moiety II, and about 14.5to about 30 mole percent each of moieties III and VII; (iii) a meltprocessable wholly aromatic polyesteramide capable of forming ananisotropic melt phase at a temperature below approximately 360° C.consisting essentially of the recurring moieties II, I, III and VIwherein: II is

IIII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety II, about 15 to about 30 mole percent each of moieties I, IIIand VI; (iv) a melt processable wholly aromatic polyesteramide capableof forming an anisotropic melt phase at a temperature belowapproximately 380° C. consisting essentially of the recurring moietiesI, II, III, VII and VI wherein: I is

II is

III is

VII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 1 to about 20 mole percent of moiety II, about 14.5to about 30 mole percent of moiety III, about 7 to about 27.5 molepercent of moiety VII, and about 2.5 to about 7.5 mole percent of moietyVI; and (v) a melt processable wholly aromatic polyesteramide capable offorming an anisotropic melt phase at a temperature below approximately350° C. consisting essentially of the recurring moieties I, II, III, IV,V, and VI wherein: I is

II is

III is

IV is

V is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 10 to about 20 mole percent of moiety II, about 2.5to about 20 mole percent of moiety III, about 0 to about 3 mole percentof moiety IV, about 12.5 to about 27.5 mole percent of moiety V andabout 2.5 to about 7.5 mole percent of moiety VI.
 29. The process as setforth in claim 27, wherein said aspect ratio (L/D) is from about 1 toabout
 3. 30. The process as set forth in claim 27, wherein said heattreatment in step (d) is carried out in stages at a final temperature ofabout 10° C. to about 15° C. below the melting transition of saidthermotropic liquid crystalline polymer.
 31. The process as set forth inclaim 27, wherein denier of said filament is from about 150 to about 500denier per filament.
 32. The process as set forth in claim 27, whereindenier of said filament is from about 180 to about 300 denier perfilament.
 33. The product produced by the process of claim
 27. 34. Theproduct produced by the process of claim
 28. 35. The product produced bythe process of claim
 29. 36. The product produced by the process ofclaim
 30. 37. The product produced by the process of claim
 31. 38. Anas-spun filament of a thermotropic liquid crystalline polymer having thefollowing properties: (a) denier of at least about 50 denier perfilament; (b) tenacity of at least about 8 grams per denier; (c) modulusof at least about 450 grams per denier; and (d) elongation of at leastabout 2 percent.
 39. The filament as set forth in claim 38, wherein saidthermotropic liquid crystalline polymer is selected from the groupconsisting of: (i) a melt processable wholly aromatic polyester capableof forming an anisotropic melt phase at a temperature belowapproximately 350° C. consisting essentially of the recurring moieties Iand II wherein: I is

and II is

wherein said polyester comprises about 10 to about 90 mole percent ofmoiety I, and about 10 to about 90 mole percent of moiety II; (ii) amelt processable wholly aromatic polyester capable of forming ananisotropic melt phase at a temperature below approximately 400° C.consisting essentially of the recurring moieties I, II, III, and VIIwherein: I is

II is

III is

and VII is

wherein said polyester comprises about 40 to about 70 mole percent ofmoiety I, about 1 to about 20 mole percent of moiety II, and about 14.5to about 30 mole percent each of moieties III and VII; (iii) a meltprocessable wholly aromatic polyesteramide capable of forming ananisotropic melt phase at a temperature below approximately 360° C.consisting essentially of the recurring moieties II, I, III and VIwherein: II is

IIII

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, II and about 15 to about 30 mole percent each of moietiesII, III and III VI; (iv) a melt processable wholly aromaticpolyesteramide capable of forming an anisotropic melt phase at atemperature below approximately 380° C. consisting essentially of therecurring moieties I, II, III, VII and VI wherein: I is

II is

III is

VII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 1 to about 20 mole percent of moiety II, about 14.5to about 30 mole percent of moiety III, about 7 to about 27.5 molepercent of moiety VII, and about 2.5 to about 7.5 mole percent of moietyVI; and (v) a melt processable wholly aromatic polyesteramide capable offorming an anisotropic melt phase at a temperature below approximately350° C. consisting essentially of the recurring moieties I, II, III, IV,V, and VI wherein: I is

II is

III is

IV is

V is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 10 to about 20 mole percent of moiety II, about 2.5to about 20 mole percent of moiety III, about 0 to about 3 mole percentof moiety IV, about 12.5 to about 27.5 mole percent of moiety V andabout 2.5 to about 7.5 mole percent of moiety VI.
 40. The filament asset forth in claim 38, wherein denier of said filament is from about 100to about 1000 denier per filament.
 41. The filament as set forth inclaim 38, wherein denier of said filament is from about 150 to about 500denier per filament.
 42. The filament as set forth in claim 38, whereindenier of said filament is from about 180 to about 300 denier perfilament.
 43. A heat-treated filament of a thermotropic liquidcrystalline polymer having the following properties: (a) denier of atleast about 50 denier per filament; (b) tenacity of at least about 20grams per denier; (c) modulus of at least about 600 grams per denier;and (d) elongation of at least about 3 percent.
 44. The filament as setforth in claim 43, wherein said thermotropic liquid crystalline polymeris selected from the group consisting of: (i) a melt processable whollyaromatic polyester capable of forming an anisotropic melt phase at atemperature below approximately 350° C. consisting essentially of therecurring moieties I and II wherein: I is

and II is

wherein said polyester comprises about 10 to about 90 mole percent ofmoiety I, and about 10 to about 90 mole percent of moiety II; (ii) amelt processable wholly aromatic polyester capable of forming ananisotropic melt phase at a temperature below approximately 400° C.consisting essentially of the recurring moieties I, II, III, and VIIwherein: I is

II is

III is

and VI is

wherein said polyester comprises about 40 to about 70 mole percent ofmoiety I, about 1 to about 20 mole percent of moiety II, and about 14.5to about 30 mole percent each of moieties III and VII; (iii) a meltprocessable wholly aromatic polyesteramide capable of forming ananisotropic melt phase at a temperature below approximately 360° C.consisting essentially of the recurring moieties II, I, III and VIwherein: I is

IIII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety II, about 15 to about 30 mole percent each of moieties I, IIIand VI; (iv) a melt processable wholly aromatic polyesteramide capableof forming an anisotropic melt phase at a temperature belowapproximately 380° C. consisting essentially of the recurring moietiesI, II, III, VII and VI wherein: I is

II is

III is

VII is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 1 to about 20 mole percent of moiety II, about 14.5to about 30 mole percent of moiety III, about 7 to about 27.5 molepercent of moiety VII, and about 2.5 to about 7.5 mole percent of moietyVI; and (v) a melt processable wholly aromatic polyesteramide capable offorming an anisotropic melt phase at a temperature below approximately350° C. consisting essentially of the recurring moieties I, II, III, IV,V, and VI wherein: I is

II is

III is

IV is

V is

and VI is

wherein said polyesteramide comprises about 40 to about 70 mole percentof moiety I, about 10 to about 20 mole percent of moiety II, about 2.5to about 20 mole percent of moiety III, about 0 to about 3 mole percentof moiety IV, about 12.5 to about 27.5 mole percent of moiety V andabout 2.5 to about 7.5 mole percent of moiety VI.
 45. The filament asset forth in claim 43, wherein denier of said filament is from about 100to about 1000 denier per filament.
 46. The filament as set forth inclaim 43, wherein denier of said filament is from about 150 to about 500denier per filament.
 47. The filament as set forth in claim 43, whereindenier of said filament is from about 180 to about 300 denier perfilament.